Problem: A square has a perimeter of $36$ millimeters. What is the area of the square?
Answer: Perimeter is the distance around a closed figure. We can find the perimeter of a shape by adding all the side lengths. The perimeter of the square is $36}\text{ mm}$. $\text{Perimeter}= 36\text{ mm}\,$ $\,$ $\,$ $\begin{aligned} P} &= {s} + {s} + {s} + {s}\\\\ 36} &= {s} + {s} + {s} + {s}\\\\ 36} &= 4 \times s \end{aligned}$ What number can we multiply by $4$ to get $36}$ ? We can divide to find the side length. $\begin{aligned} 36}\div4 = {\text{s}}\\\\ 9={\text{s}} \end{aligned}$ Now, we can find the area. $\begin{aligned} \text{Area} &= \text{side} \times \text{side}\\\\ &= {s} \times {s}\\\\ &= {9} \times {9}\\\\ &= 81\text{ square mm} \end{aligned}$ The area of the square is $81$ square millimeters.